1. Field of Invention
The invention is related to a pulley set for a continuously variable transmission unit, comprising a pair of discs accommodated on a shaft, and a screw mechanism which is concentric with respect to said discs and for moving the discs towards and from each other, said discs enclosing a V-shaped groove, for accommodating a belt, said screw mechanism being controllable by a controller, wherein said controller includes a motor unit, said motor unit including a stator and a rotor, one of said stator and rotor engaging the nut of the screw mechanism, and the other of said stator and rotor engaging the screw of the screw mechanism, the controller having two linked satellite gear wheel systems, one of which connects the rotor or the stator to the nut, and the other of which connects the other of said rotor or the stator to the nut, and the other of which connects the other of said rotor or stator to the screw, said satellite gear wheel systems each comprising a ring gear wheel, a sun gear wheel and satellite gear wheels.
2. Description of Related Art
A continuously variable transmission having such pulley sets is known from EP A 582307. The screw mechanisms of the pulley sets are controlled by a common, single motor, which is offset with respect to said screw mechanisms. The motor engages the screw mechanism through a number of intermediate gear wheels and auxiliary shafts.
As a result, this prior art continuously variable transmission unit is complicated, and therefore prone to malfunction. Moreover, its overall dimensions are rather large.
The object of the invention is to provide a pulley set for a continuously variable transmission, which does not have these disadvantages. This object is achieved in that the sun gear wheels or the ring gear wheels are fixedly connected together.
The pulley set according to the invention may have its own motor unit. This allows a rapid and independent control of the gap of the pulley set. As a result, the pinching force exerted by the discs on the belt can be regulated as required, in particular in order to avoid slip. Also, a rapid transmission ratio change is made possible.
In case the screw mechanism is static in relation to the nut, the screw mechanism and the nut have the same rotational speed. The transmission ratio is then constant, and the motor keeps the screw mechanism, and thus the discs of the pulley set, in a static position. That is, the discs enclose a gap which remains of constant width.
Upon a relative rotation between the rotor and the stator of each motor, a change in said gap is generated due to the action of the screw mechanism.
The required reduction between the motor and screw mechanism is preferably obtained by means of at least one satellite gear wheel system. For instance, each controller may comprise two linked satellite gear wheel systems, one of which connects the rotor or the stator to the nut, and the other of which connects the other of said rotor or stator the screw, said satellite gear wheel systems each including a ring gear wheel, a sun gear wheel and satellite gear wheels.
The pulley set having two linked satellite gear wheel systems may be carried out in several ways.
According to a first embodiment, the ring gear wheels are connected to the stator respectively to the rotor, and the sun gear wheels are connected to each other.
According to a second embodiment, the sun gear wheels are connected to the stator respectively to the rotor, and the ring gear wheels are connected to each other.
According to a third embodiment, the satellite gear wheels of each satellite gear wheel system are accommodated on a respective carrier, said carriers being connected to the stator respectively to the rotor, and the sun gear wheels are connected to each other.
According to the fourth embodiment, the satellite gear wheels of each satellite gear wheel system are accommodated on a carrier, said carrier being connected to the stator respectively to the rotor, and the ring gear wheels are connected to each other.
The gear ratios of the satellite gear wheel systems should be identical.
Preferably, the satellite gear wheel systems are coaxial and have coaxial ring gear wheels and coaxial sun gear wheels.
The diameters of the ring gear wheels can be identical. Also, the diameters of the sun gear wheels can be identical, and the diameters of the satellite gear wheels can be identical.
The sun gear wheel of a satellite gear wheel system may be connected to the shaft, and the ring gear wheel of a satellite gear wheel system may be connected to the shaft. Also, the carriers for the satellite gear wheels may be connected to the shaft.
Preferably, an electric motor is applied in the controller, which may be concentric with relation to the pulley set.
The invention also relates to a continuously variable transmission including two pulley sets as described before and an endless belt stretching between said sets and accommodated in the grooves thereof.